Matrices for the stabilizing and controlled release of problematic substances

ABSTRACT

The invention concerns a carrier system for stabilizing and controlled release of active substances, in particular problematic pharmaceutical substances in a biological environment. Said carrier system comprises a lipid matrix having water solubility corresponding to one part of the lipid matrix for 30 parts of water, and at least a release controlling substance, said substance being insoluble in the lipid matrix.

The present invention relates to carrier systems for problematic activesubstances such as sensitive medicaments, which both ensure thestability of the active substances and at the same time allow releaseover a period of days, weeks or months.

Problematic active substances such as sensitive medicaments, for exampleproteins, peptides and even some cytostatics, are characterised by veryshort half-lives in biological media that are sometimes in the region ofonly a few minutes. Only a very short duration of action can anticipatedwhen sensitive medicaments such as this are introduced into the body. Asa result, a great many therapeutically interesting medicaments neverquite reach the stage of processing to produce effective and potentdrugs. As early as the beginning of the 70s, these substances began tobe protected from accelerated degradation by slow release from arepository; at the same time prolonged release from a matrix began to beused.

Polymers in particular have been investigated very intensively for theirsuitability as a matrix for the parenteral administration of sensitivemedicaments. A great many compounds were simultaneously synthesised forthis purpose. Alongside synthetic materials such as, for example,poly(α-hydroxy esters) or polyanhydrides, natural materials such as e.g.collagen or alginate are also increasingly being used.

The feature common to all these substances is that the active substancesto be protected during parenteral administration are released from arepository in a controlled manner. Due to these developments, a numberof therapeutically relevant substances such as, for example, LHRHagonists, somatotropin or human growth hormone have been successfullymarketed as pharmaceutical forms. This is, however, only a relativelysmall proportion of the medicaments for which this technology would besuitable.

The reasons for this reside in the problems which arise when polymers,in particular ones which are biodegradable, are combined with activesubstances in protein medicaments. Thus, in the commonly usedpoly(α-hydroxy esters) incompatibility reactions arise between thepolymer and the protein or peptide medicaments. One might cite in thisregard the low pH which is possible within polymer matrices of thistype. These pH values have been reported to be in the region of 2, andthey therefore have a detrimental effect on some protein medicamentswhich leads to a loss of biological activity.

It has furthermore been established that, during degradation of thepolymer matrix, in the course of which the corresponding oligomers andmonomers are released, an accumulation of these degradation productsoccurs.

On account of this accumulation of degradation products, the osmoticpressure within the matrix is increased to 2 to 3 times the osmoticpressure of the serum or of an isotonic saline solution.

In the specific case of poly(α-hydroxy esters), such as e.g. poly(lacticacid) (PLA) or poly(lactic acid-co-glycolic acid) (PLGA) andpolyanhydrides, it has also been found that the monomers occurring inthe course of degradation of the polymer are covalently bound tofunctional groups of the active substances, for example amino groups.The reaction with polymers and/or polymeric degradation products,non-physiological pH and osmotic pressure values, can influence, and toa considerable degree impair, the efficacy and tolerability of proteinand peptide medicaments.

The natural polymers include a number of substances which do not exhibitthese problems, e.g. collagen, gelatins or alginate as hydrogel-formingpolymers, which in the presence of water form systems with increasedviscosity and in some cases elasticity. The same is true of synthetichydrogel-forming polymers, such as cellulose ethers, polyvinyl alcoholand derivatives of polyacrylic acid. Such materials do have otherdisadvantages, however.

In many cases, an undesirably rapid release of the incorporated activesubstances occurs. As a result, it is almost impossible to releasesubstances over longer periods of time, for example weeks or months. Toachieve this, the polymer chains have to be cross-linked. Cross-linkingsubstances such as e.g. aldehydes have been used for this purpose. It isnot possible to use substances of this type for protein and peptidemedicaments, however.

When alginate is used, undesirable ionic interactions with the alginatechains or the bivalent metal ions used for cross-linking, e.g. calciumions, may also occur.

Once cross-linking has been performed, charging is very complicated,however. Charging is usually carried out by incubating the polymer in apeptide or protein solution. However, the time needed for thiscorresponds roughly to the release time, and is therefore uneconomicallylong.

Many of the materials mentioned above also have the disadvantage thatthey undergo considerable expansion; this greatly impedes and limitstheir use in many tissues, such as the brain, which is especiallysensitive to pressure.

It has been known to use lipids for the release of medicaments. However,lipids in general have only a limited capacity for the controlledrelease of active substances. Trials were therefore conducted withcontrol of the release of the active substances via the composition ofthe lipid matrices.

Thus U.S. Pat. No. 4,452,775 describes the use of different qualities ofcholesterol. U.S. Pat. No. 4,610,868 describes the use of surface-activesubstances which cause the matrices to “dissolve”, thereby controllingtheir release from the matrices. In these systems, release control isachieved by working lipids up with one another and with substances thatare miscible with one another or at least partially soluble in oneanother. This can be recognised for example from the fact that in eachcase, after working up these substances, no separation into theindividual components occurs. If spatial separation of the individualcomponents is a necessary consequence of the type of processing, forexample the compression of powders, the substances are nevertheless atleast partially soluble in one another and are in addition characterisedby the fact that, in water, they are “sparingly soluble” (less than 1part of the substance dissolves in 30 to 100 parts of water) to“practically insoluble” (less than 1 part of the substance dissolves in10,000 parts of water).

The use described in the literature to date, of substances that arepartially soluble in lipids to modify the release from lipid matrices,is associated with a number of serious disadvantages. To give anexample, a change in the properties of the lipid occurs; this may be achange in its physical characteristics, such as a shift in the meltingpoint. Furthermore, this kind of release modification offers onlylimited scope to vary the release without fundamentally altering thesystem.

U.S. Pat. No. 4,610,868 describes, for example, the use of surfactantswhich may, however, have a disadvantageous influence on the structure ofthe proteins, e.g. on their tertiary structure, and may even causeunfolding.

The disadvantage with many of the known systems is their high content ofthe medicament. Thus U.S. Pat. No. 5,801,141 describes the production ofa lipid matrix for the parenteral administration of growth factors,which is 20 to 80% charged with the active substance. The ratio ofactive substance to lipid in such cases is 0.7 and above.

U.S. Pat. No. 4,985,404 describes systems consisting of oils having apolypeptide content of at least 10%. Such a high charge is unnecessaryfor many applications and is not economical. Furthermore, if theactive-substance charge is very high, the desired controlled release isno longer guaranteed.

The above carrier systems for problematic medicaments thus all haveserious disadvantages which may lead on the one hand to impairment ofthe stability of the active substances and on the other to a releasewhich is difficult to control, especially when the aim is release overweeks and months

The aim of the invention was to provide a biologically safebiodegradable and bioerodable carrier system for the controlledadministration of problematic active substances, in particularproblematic medicaments. The aim of the invention was in particular toprovide a carrier system of this type for parenteral administration.

According to the invention, an alternative was in particular to be foundto the known biodegradable polymers for the release of protein andpeptide medicaments which enables a controlled release of activesubstances of this type in vivo over days, weeks and months; inaddition, the matrix material itself was to have adequate stability invivo and at the same time create an environment for the guest moleculeswhich does not impair their stability. With the carrier system, it wasalso to be possible to provide release systems for medicaments withwhich administration is also possible by injection.

This aim is achieved by means of a carrier system for active substances,in particular medicaments, containing at least one lipid matrix whichhas a solubility in water of one part lipid matrix in at least 30 ormore parts of water and at least one release-controlling substance whichis insoluble in the lipid matrix.

The present invention also relates to a composition containing thecarrier system according to the invention and at least one activesubstance.

The invention relates in particular to carrier systems of this type andto pharmaceutical compositions for problematic active substances such asproblematic medicaments.

With the carrier system according to the invention, any activesubstances may be introduced into biological environments such as thosepresent in the bodies of humans and animals, and released there in acontrolled manner.

Controlled release means that the active substance is releasedcontinuously or discontinuously into the environment over a desired timeperiod.

According to the invention, the carrier system is preferably solid atbody temperature and does not melt in the body.

Problematic active substances such as problematic medicaments within thescope of the invention are active substances or medicaments which haveonly very short half-lives in biological media and/or have only a narrowrange of local tolerability and/or a low therapeutic index. Inparticular they are active substances having a half-life of less thanone hour, in particular of only a few minutes. They may be activesubstances which degrade easily even at room temperature or underenvironmental conditions, and/or which are subject to rapid localenzymatic degradation in vivo.

A low therapeutic index means that the active substances must beadministered in very precise dosages in order to avoid toxic effects, asthe gap between therapeutic and toxic doses is small.

Examples of problematic medicaments of this type are proteins, peptides,antisense oligonucleotides, bisphosphonates, and even some cytostatics.Thus the cytostatic carmustine (BCNU) in plasma has a half-life of onlyapproximately 20 minutes. Other examples are the enzyme hyaluronidaseandD-arginyl-L-arginyl-L-prolylglycyl-3-(2-thienyl)-L-alanyl-L-seryl-(3R)-1,2,3-tetrahydro-3-isoquinolinocarbonyl-(2S,3aS,7aS)-octahydro-1H-indo-1-2-carbonyl-L-arginine,also called “HOE 140”, insulin, growth factors and cytokines, e.g. fromthe BMP family or the IGF family, and substances such as FGF, EGF, PDGF,NGF, BDNF and GDNF, erythropoietin, somatostatin and atrial natriureticpeptide.

Further examples are doxorubicin, 4′-epi-doxorubicin, 4 or4′-desoxydoxorubicin or a compound preferably from the group etoposide,N-bis(2-chloroethyl)-4-hydroxyaniline, 4-hydroxycyclophosphamide,vindesine, vinblastin, vincristine, terfenadine, fexofenadine,terbutaline, fenoterol, salbutamol, muscarine, oxyphenbutazone,salicylic acid, p-aminosalicylic acid, 5-fluorouracil, methotrexate,diclofenac, flufenaminic acid, 4-methylarninophenazone, theophylline,nifedipine, mitomycin C, mitoxantron, camptothecin and camptothecinderivatives, m-AMSA, taxol, docetaxel, nocodaxol, colchicine,cyclophosphamide, rachelmycine, cisplatin, melphalane, bleomycin,nitrogen-mustard gas, phosphoramide mustard gas, verrucarin A,neocarcinostatin, calicheamicin, dynemicin, esperamicin A, quercetin,genistein, erbstatin, tyrphostine, rohitukin derivative, retinolic acid,butyric acid, phorbol ester, dimethylsulfoxide, aclacinomycin,progesterone, busereline, tamoxifen, mifepristone, onapristone,N-(4-aminobutyl)-5-chloro-2-naphthalenesulfonamide,pyridinyloxazol-2-one, quinolyloxazol-2-one, isoquinolyloxazol-2-one,staurosporin, ethanolamine, verapamil, forskoline,1,9-dideoxyforskoline, quinine, quinidine, reserpine, ramipril,teicoplanin, risedronate, irinotecan, glatriamer acetate, riluzol,glimeperide, 18-O-(3,5-dimethoxy-4-hydroxybenzoyl) reserpate,lonidamine, buthionine sulfoximine, diethyldithiocarbamate, cyclosporinA, rapamycin, azathioprin, chlorambucil, hydroxycrotonic acid amidederivative-2, leflunomide, 15-deoxyspergualine, FK 506, ibuprofen,indomethacin, aspirin, sulfasalazine, penicillamine, chloroquine,dexamethasone, prednisolone, mefonamidic acid, paracetamol,4-aminophenazone, muskosin, orciprenaline, isoprenaniline, amiloride andp-nitrophenylguanidine benzoate.

It will be understood that the present invention is not limited to theaforementioned examples, but is generally applicable to activesubstances, in particular active substances the administration of whichis associated with the aforementioned problems.

The carrier system according to invention has a lipid matrix composed ofone or more lipids, the lipid matrix being sparingly soluble topractically insoluble in water. This means that one part of the lipidmatrix is soluble in 30 parts or more of water.

For the definition of solubility in water, according to the inventionreference is made to the relevant information in the EuropeanPharmacopoeia, vol. 1, general section, 4^(th) edition, Grundwerk 2002,Deutscher Apothekerverlag Stuttgart, Govi-Verlag-Pharmazeutischer VerlagGmbH Eschbom, page 6. According to the classification given therein,sparingly soluble to practically insoluble means that one part of thelipid matrix is soluble in 30 parts or more of water, in particular in30 parts to 10,000 parts of water.

The carrier systems according to invention preferably exhibit nopronounced expansion and thus no marked weight increase in water. Thusthe weight increase in water due to swelling is preferably below 20%, inparticular below 10%, and especially preferably below 5%.

Because swelling is slight, the carrier systems according to theinvention may also be used in pressure-sensitive regions of the body.

Examples of lipids are monoglycerides, diglycerides and triglycerides,the esters of glycerol, and fatty acids. The glycerol may be esterifiedwith the same fatty acid or with different fatty acids.

Essentially any fatty acids may be used.

The length of the carbon chain of the fatty acid is determined by thetype of carrier system required. Short-chain fatty acids generally leadto free-flowing to liquid systems and, correspondingly, longer-chainones to solid systems. For parenteral administration especially solidcarrier systems are desirable, and correspondingly longer-chain fattyacids may be used. Suitable examples are fatty acids having 12 or morecarbon atoms.

The fatty acids should furthermore exhibit adequate stability, in viewof which saturated fatty acids are preferred.

Examples of suitable glycerides are glyceryl trilaurate C12, glyceryltrimyristate with C14, glyceryl tripalmitate with C16, glyceryltristearate C18 etc.

Other examples of suitable lipids are substances which according to theliterature are known to the person with ordinary skill in the artoverall as lipids, such as wax alcohols, fatty acids, ceramides,cholesterol, sphingolipids, phospholipids or lecithin.

Waxes may also be used. Examples are vegetable and animal waxes such ascarnauba wax, beeswax, shellac wax or spermaceti. Synthetic waxes mayalso be used, the basic chemical structure of which corresponds to thatof the natural waxes, e.g. synthetic spermaceti.

Lipids as defined by this invention also include synthetic orsemi-synthetic substances which are biologically safe and have therequisite low solubility in water according to the invention. The lipidsused according to the invention may also be corresponding substanceswhich are known from the metabolism of fat. Examples of lipids of thistype are described in U.S. Pat. No. 5,785,976, U.S. Pat. No. 6,120,789and U.S. Pat. No. 5,888,533, to which reference is expressly made inthis regard.

The advantage of the lipids used according to the invention is that, onaccount of their low solubility in water, they form matrices which arestable for lengthy periods in water or an aqueous biological medium, orrepresent systems which partially erode with the formation ofcolloid-disperse systems.

The lipids according to invention are thus stable in water, but arebroken down in a biological environment. The degradation in a biologicalenvironment may, for example, be enzymatic, or it may take place due tonatural metabolic processes.

Surprisingly it has been shown that problematic active substances suchas problematic medicaments are stabilised by the lipid matrices usedaccording to the invention.

Thus the lipids used according to the invention, in contrast withbiodegradable polymers, characterised in that they do not form covalentbonds with the active substances used. Moreover, the erosion of thelipid matrix according to the invention is not associated with anincrease in the osmotic pressure or a decrease in the biological pH inor around the carrier.

Surprisingly, it has been shown that although lipids such as those fromthe glyceride series have hydrolysable ester bonds leading, in the caseof the poly(α-hydroxy esters), to the acylation of amino groups, unlikepolymers they do not give rise to a significant increase in the osmoticpressure, a lowering of the pH, acylation of proteins or pronouncedswelling.

The carrier system according to invention furthermore contains arelease-controlling substance which governs and controls the releasekinetics of the active ingredient. By the addition of the at least onerelease-controlling substance, even in the case of lipids it is possibleto achieve a desirable release profile over a period of days, weeks ormonths.

The release-controlling substance used according to the invention is asubstance which is not soluble in the lipid matrix or is not miscibletherewith. Surprisingly, substances which are not soluble or misciblewith the lipids were found to be especially advantageous for controllingthe release kinetics of active substances in lipids and therefore formodifying their release. According to the invention, substances with asolubility in the lipid matrix of one part of substance to at least10,000 parts of lipid are used for this purpose.

The solubility of the release-controlling substance in the lipid matrixis similarly classified in accordance with the solubility data given inthe commentary to the German Pharmacopoeia, 7^(th) edition 1968,Wissenschaftliche Verlagsgesellschaft mbH Stuttgart, Govi-Verlag GmbHFrankfurt, pages 8 and 9.

The release-controlling substances used according to the invention havea solubility in water of 1 part of substance to 1 to 10 parts of water,in particular 10 to 30 parts of water, and may thus be classified assoluble to freely soluble.

The release-controlling substances used according to the invention maybe low-molecular freely to very freely water-soluble substances selectedfrom among electrolytes, monosaccharides and disaccharides, and aminoacids such as e.g. glycine. Examples of suitable electrolytes arecombinations of cations and anions from the Hofmeister series, such asthose described in “Peptide and protein delivery”, V. H. L. Lee (ed.),Marcel Dekker 1991, page 179. Preferred examples of cations are Mg²⁺,Li²⁺, Na⁺, K⁺, NH⁴⁺, Zn²⁺ and Ca²⁺, and anions (SO₄)²⁻, (HPO₄)²⁻,CH₃COO⁻, Cl⁻, (NO₃)⁻ and I⁻.

Suitable examples of monosaccharides are glucose, fructose, galactoseand mannose. Suitable examples of disaccharides area trehalose,gentiobiose, maltose, saccharose and lactose.

Sugar alcohols may also be used. Examples are sorbitol and mannitol.

Polymers have proved especially suitable. Suitable polymers have thecapacity to swell in water, and thus to undergo a volume increase. Byway of example one may cite polymers from the class of thehydrogel-forming polymers, the polysaccharides, proteins and peptides,the polyethers and the polyesters. The following substances may be usedinter alia: gelatins, traganth, methyl cellulose, polyvinylpyrrolidone,agar, alginates and their salts, gum arabic, methyl cellulose,hydroxyethyl cellulose, carboxymethylcellulose, hydroxymethyl cellulose,methylhydroxypropyl cellulose, hydroxypropyl cellulose, chitosan,scleroglucans, polyacrylates or methacrylates and their copolymers,polyacrylamides, pectin, starch and starch derivatives, polyvinylalcohol, polyethylene oxide, dextran and heparin.

Polyethylene glycol, hydrogel-forming polymers such as gelatins,alginate and collagen are especially preferred.

Non-animal polymers are also preferably used according to the inventionfor the release-controlling substance.

Examples of non-animal polymers are cellulose derivatives such ascellulose ethers, inter alia methyl cellulose, hydroxypropyl methylcellulose and carboxymethyl cellulose, polyvinylpyrrolidone, andpolyvinyl alcohol.

The content of the release-controlling substance in the carrier systemaccording to the invention is usually within a range from 0.001 to 30%(m/m), with reference to the lipid matrix fraction; preferably within arange from 0.01 to 20% (m/m), and especially preferably 0.1 to 10%(m/m).

The content of release-controlling substance in the carrier systemaccording to the invention represents a simple means whereby the rate ofrelease of the carrier system for an active ingredient may becontrolled. The determination of a suitable content as a function of thetype of lipid matrix and active substance used is a routine practicewhich is within the capability of the person with ordinary skill in theart.

In order to adjust the desired small weight increase and thus swellingof the carrier system according to the invention in water, when usingpolymers which expand greatly it may be necessary to use the latter onlyin a small proportion or to use the polymers in a form which is notsubject to pronounced swelling.

To this end, the polymers may, for example, in the first instance beswollen up in water, and the fully swollen gels obtained thenfreeze-dried. The polymers may then be used after appropriatecomminution, without further swelling taking place.

The ratio of active-substance content to lipid content according to theinvention is below 0.7 and especially 0.5 (expressed as a weight ratio)in order to ensure adequate stabilisation.

The carrier system preferably contains 30 wt. % or less, especially 15wt. % or less, and especially preferably less than 10 wt. % of theactive substance, and especially 5 wt. % and less (with reference to thecarrier system).

Particularly in the case of low active-substance contents of less than10 wt. %, the release occurs by diffusion processes, during which thedesired release profile may be especially advantageously established.

The erosion duration of the carrier system according to the inventionmay, if required, also be shortened by addition of surface-activecompounds. Examples of surface-active compounds of this type arecholesterol, glycerophospholipids and sphingophospholipids.

By this means, for example by adding phospholipids to a matrix oftriglyceride, the erosion of the matrix may be accelerated in vivo.

These surface-active compounds may be used in a content within a rangeof up to 90 (w/w), and in particular 0.5 to 50 (w/w), with reference tothe lipid matrix.

Thus the degradability of the carrier system according to the inventionin vivo may be altered not only via the composition of the lipid matrixor of the carrier system, but also with the use of suitable additives.

It will be understood that other additives, such as those known for usein release-controlling systems, may be added if required.

Such additives may be, inter alia, other problematic medicaments,stabilising compounds such as electrolytes and buffering substances.

According to another embodiment, the active substance itself may act asa release-controlling substance, thereby completely or partiallyreplacing the latter within the carrier system. In this case, theactive-substance content may be 1 wt. % or more, in particular 2 wt. %or more, with reference to the carrier system.

Examples of active substances which are suitable for this purpose areinsulin, growth factors of the BMP family such as BMP-2, growth factorIGF and erythropoietin (EPO).

The carrier system according to the invention may be available foradministration in any geometric shape. They are usually round, oval orcylindrical.

The carrier system may be a multi-layer system, in which a hollow orsolid core is surrounded by further layers. The individual layers may becharged with the same or with different active substances; individuallayers may also be active substance-free. The active substance may bepresent in the individual layers in the same or in differing amounts.

In this respect the carrier system may be designed in accordance withrequirements and the desired dosage form.

Depending on the dosage form, the carrier system according to theinvention may be solid to semi-solid. For example, the carrier systemfor injection may be used in a semi-solid form.

For use in humans or animals, the carrier system should not melt. Themelting point of the carrier system according to the invention istherefore preferably above 40° C., especially 60° C. or more.

The carrier system may be manufactured and charged using the methods forthis purpose which are known per se. For example, it may be manufacturedby extruding the active substance and the material for the carriersystem.

The carrier system is advantageously manufactured and charged by firstof all melting the lipid or lipid mixture. The active substance in thesolid or undilute form is then stirred into the melt, forming asuspension. If applicable, the release-controlling substance may bemixed in at the same time. The suspension obtained can then be worked upinto the desired form.

If required, an organic solvent may be added to the lipid mixture toimprove the homogenisation of the lipids; the organic solvent is removede.g. by evaporation prior to addition of the active substance.

In contrast with known methods, in which the active substance is firstof all dissolved in a solvent, according to the invention the carriersystem can therefore be charged with active substance without the activesubstance coming into contact with a solvent. This is especiallyadvantageous in the case of active substances which exhibit lowstability in contact with a solvent such as water, etc.

A solid active substance may be added in the form of particles ofsuitable granule size, which varies according to requirements. The meangranule size is usually in general less than 1000 μm.

Especially advantageous is the addition of the active substance in amicronised form, with a mean granule size of <10 μm, especially <5 μmright into the nanometre range.

Similarly the release-controlling substance may be added in the form ofparticles of suitable size.

The working up of the active substance and of the release-controllingsubstance to form particles such as microparticles of the required sizemay be performed by methods conventionally used for this purpose. Forexample, the comminution may be performed by milling in suitable mills.

The carrier system according to the invention may advantageously be usedto produce pharmaceutical compositions.

Depending on the choice of active substance or pharmaceutical substanceemployed, the pharmaceutical composition may be used to release theactive substance or pharmaceutical substance in vitro or in vivo inliving organisms such as humans or animals such as the horse, dog,rabbit, cow, mouse, rat, etc.

Due to the stabilisation of the active substance which, according to theinvention, is also possible over a long period, even in regions wheremedical facilities are poor, living organisms may be treated by means ofa single administration of the pharmaceutical composition by a doctorand supplied with necessary problematic medicaments over a lengthyperiod without further involvement of the doctor. If, for example, aplurality of administrations separated by time intervals are necessary,the release may be controlled accordingly by the provision ofcorrespondingly active substance-free portions in the pharmaceuticalcomposition alongside portions which contain active substance.

The function and mode of action of the carrier system according to theinvention will be made especially clear on the basis of the embodimentsshown in the drawings.

The figures are as follows:

FIG. 1: A diagram showing the stabilising action of the lipids usedaccording to the invention in respect of proteins;

FIG. 2: A diagram comparing the efficacy of BCNU in tumour-bearing nudemice for lipid matrices according to the invention and in conventionalpolyanhydride matrices;

FIGS. 3 and 4: Diagrams showing modification of the rate of release inthe carrier system according to the invention as a function of thecontent of release-controlling substance, and

FIG. 5: Images of a carrier system according to the invention obtainedin vivo over a period of 15 days.

FIG. 1 is a diagram in which the activity of the enzyme hyaluronidase ina conventional carrier system composed ofpoly(1,3-bis[carboxyphenoxypropane]-sebacic acid is shown to be 20:80 ofthe activity of this enzyme in the matrix composed of glyceryltripalmitate as the lipid. Whereas the release of the enzyme from theconventional system leads to inactivation, in the case of in-vivorelease from the glyceryl tripalmitate matrix 100% of the activity isachieved. This shows that proteins are in principle stabilised by lipidssuch as those used according to the invention for the carrier system,and also retain their activity over a longer period.

The ordinate gives the release quantity of hyaluronidase in percent, andthe abscissa the time in hours.

Apart from stabilisation of problematic active substances, the carriersystems according to the invention are also characterised by bettertolerability in a biological system by comparison with numerous polymerssuch as are conventionally used for carrier systems. In this regard,reference is made to the deposition of monomers, the degradationproducts of polymer-based carrier systems, and oedematisation followingthe application within the central nervous system (CNS) of polymericimplants containing cytostatics. Problems of this type are caused, interalia, by the use of polyanhydrides, for examplepoly(1,3-bis[carboxyphenoxypropane]-co-sebacic acid) in a ratio of20:80.

Polyanhydrides are used within the CNS mainly in the treatment ofglioblastoma multiforme, for protecting the hydrolysis-sensitive activesubstance BCNU from inactivation due to water. However, the use ofpolyanhydrides can lead to an accumulation of monomers within the CNSwhich persists for months and can lead to local irritation and evenoedema.

According to the invention it has been found that with the use oflipids, as with conventional polyanhydrides, the diffusion of water intoa matrix can be slowed and the stability of the active substance in vivoguaranteed. Thus the effectiveness of BCNU in tumour-bearing nude mice(U78 MG tumour subcutaneously inoculated) is the same for a lipid matrixaccording to the invention and for a conventional polyanhydride matrix,as shown in FIG. 2.

In FIG. 2, the area of the tumour is plotted in nm² on the ordinate, andthe time in days on the abscissa.

This shows that, in addition to the already described stabilisation ofproblematic medicaments, the harmful effects of polymers on tissue canalso be prevented. Lipids such as, for example, cholesterol are anatural constituent of tissues in the CNS, in contrast with theconventionally used polymers such as the polyanhydrides.

Other materials from the lipid group may be converted or broken downnaturally within the biological system in the metabolism, withoutinfluencing physicochemical parameters such as the pH or the osmoticpressure.

On the basis of the above-mentioned knowledge concerning the efficacy ofthe lipids used according to the invention, it is for example possibleto replace polyanhydrides in implants, such as those described forexample in U.S. Pat. No. 6,086,908, or in microparticles or implants foruse within the CNS.

FIGS. 3 and 4 show diagrams illustrating the dependence of the rate ofrelease on the proportion of release-controlling substance in thecarrier system according to the invention. In the embodiment shown inFIGS. 3 and 4, a lipid matrix composed of glycerol tripalmitate withdiffering gelatin contents is used as the release-controlling substance.The carrier system used is cylindrical in shape. FIG. 3 shows thecontrolled release of pyranine, a low-molecular fluorescent pigment,over a period of several weeks, and FIG. 4 the release of bovine serumalbumin fluorescence-labelled with tetramethylrhodamine (TAMRA-BSA). Inboth cases release of the active substance over a number of weeks ormonths is possible.

The proportion of gelatin within the carrier system is 0, 1, 5, 10 and20%.

The quantity released in percent is shown on the ordinate, and the timein days on the abscissa.

The release which is possible in vivo according to the invention evenover long periods from the carrier systems according to the invention isalso ensured in that the carrier systems per se are similarly stableover long periods in vivo.

Thus experiments with nude mice demonstrate that, following subcutaneousimplantation of carrier systems based on glyceryl trimyristate, nosignificant change in the geometry of the carrier system is detectableeven after 15 days (FIG. 5). The images in FIG. 5 show the carriersystem after 0, 1, 3, 8 and 15 days, the numbers above the imagesrepresenting the number of days.

As shown above, by combining lipids having differing physicalproperties, solid carrier systems may be obtained and worked up to formimplants or microparticles, or semi-solid systems may also be produced,which are especially suitable for administration e.g. with the aid of aneedle. The examples given below are intended to further illustrate thepresent invention.

EXAMPLE 1

Production of an insulin-charged carrier system

To produce insulin-charged lipid microparticles based on glyceryltripalmitate, the proteins were dispersed as a solid substance in a meltof the lipid.

To this end, the lipid was heated to at least 5° C. above the meltingpoint (approximately 70° C.). The insulin present as the solid substancewas dispersed in the melt with the use of an Ultraturrax atapproximately 10,000 rpm for one minute. The dispersion obtained wasthen sprayed with a single-substance nozzle. The particles which formedsolidified due to cooling in air.

To influence the release of the active substance by means of arelease-controlling substance, the active substance and therelease-controlling substance were first of all worked up to form anaqueous solution. When using gelatin as the release-controllingsubstance, an approximately 5% gel (m/m) was first of all produced bydissolving the active substance. The gel was then freeze-dried. Theresulting solid substance was thereafter dispersed in a lipid melt asdescribed above, and worked up to form particles.

EXAMPLE 2

Substances used for the release from the carrier system (for examplepyranine or tetramethylrhodamine-labelled bovine serum albumin(TAMRA-BSA) were dispersed in the desired quantity in an aqueous 15%(m/m) gelatin solution. 100-μl portions of this dispersion were pipettedinto each opening in a 96-hole plate, and freeze-dried. The lyophilisatewas comminuted in a mortar, and mixed with glyceryl trimyristate in adesired percentage. Powder mixtures with a content of up to 30% (m/m) ofgelatin resulted. Cylindrical carrier systems were produced bycompressing the corresponding proportions by weight of gelatin withlipid granulate. To this end, 7 mg of substance was produced in a 2-mmpressing tool using a compressive force of 250 N over 10 sec. In thisway, carrier system charged with pyranine or fluorescence-labelledbovine serum albumin (TAMRA-BSA) were produced in the composition, asshown in Table 1. TABLE 1 Composition of carrier systems charged withpyranine or TAMRA-BSA Glyceryl trimyristate Gelatin [mg] [mg] Pyranine[mg] 6 — 194 6  2 192 6 10 184 6 20 174 6 40 154 TAMRA-BSA [mg] 2 — 98 2 1 97 2  5 93 2 10 88 2 20 78

EXAMPLE 3

To test the release of model substances from carrier systems dependingon the content of release-controlling substance, the cylinders obtainedin Example 1 were incubated at 37° C. in 40 ml of phosphate buffer at pH7.4. The release of the substances was monitored by measuring thefluorescence intensity. To this end, pyranine was excited at 407 nm andthe emission measured over 436 nm. The TAMRA-BSA content was determinedat a wavelength of 572 nm with excitation at 541 nm. FIG. 3 shows therelease of pyranine (mean values for n=5), FIG. 4 the release ofTAMRA-BSA (mean values for n=4). The two figures confirmed that therelease of the substances is optimally controlled via the gelatincontent.

EXAMPLE 4

To test the stabilising properties of the carrier systems, glyceryltrimyristate was worked up with hyaluronidase. To this end, 25 mgneopermease, a mixture of 200,000 IU hyaluronidase and gelatin, wasmixed with 325 mg of lipid and compressed as described in Example 1 toform cylindrical carrier systems weighing 7 mg. The gelatin content ofthis mixture was approximately 7.1%. To determine the release of theenzyme, 5 matrices were incubated with phosphate buffer as described inExample 2, and the release determined by measuring the activity via theMorgan-Elson reaction (Muckenschnabel I., Cancer Lett. 131(1) (1998) 13to 20). FIG. 1 shows that all the activity is liberated; thus the enzymewas stabilised in the carrier system.

1. A carrier system for the stabilization and controlled release ofactive substances, the carrier system comprising: at least one lipidmatrix having a solubility in water of 1 part of lipid matrix in atleast 30 parts or more of water; and at least one release-controllingsubstance which is insoluble in the lipid matrix.
 2. The carrier systemaccording to of claim 1, wherein the carrier system does not melt inbiological environments.
 3. The carrier system of claim 1, wherein thesolubility of the release-controlling substance is 1 part of substanceto at least 10,000 parts of lipid matrix. 4-19. (canceled)
 20. Thecarrier system of claim 2, wherein the solubility of therelease-controlling substance is 1 part of substance to at least 10,000parts of lipid matrix.
 21. The carrier system of claim 1, wherein therelease-controlling substance has a solubility in water of 1 part ofsubstance to 30 parts of water or less than 30 parts of water.
 22. Thecarrier system of claim 2, wherein the release-controlling substance hasa solubility in water of 1 part of substance to 30 parts of water orless than 30 parts of water.
 23. The carrier system of claim 3, whereinthe release-controlling substance has a solubility in water of 1 part ofsubstance to 30 parts of water or less than 30 parts of water.
 24. Thecarrier system of claim 20, wherein the release-controlling substancehas a solubility in water of 1 part of substance to 30 parts of water orless than 30 parts of water.
 25. The carrier system of claim 1, whereinthe release-controlling substance is selected from among polymers of theclass of the hydrogel-forming polymers, the polysaccharides, theproteins and peptides, the polyethers and polyesters, an electrolyte andmonosaccharides and disaccharides and amino acids, as well ascombinations thereof.
 26. The carrier system of claim 2, wherein therelease-controlling substance is selected from among polymers of theclass of the hydrogel-forming polymers, the polysaccharides, theproteins and peptides, the polyethers and polyesters, an electrolyte andmonosaccharides and disaccharides and amino acids, as well ascombinations thereof.
 27. The carrier system of claim 3, wherein therelease-controlling substance is selected from among polymers of theclass of the hydrogel-forming polymers, the polysaccharides, theproteins and peptides, the polyethers and polyesters, an electrolyte andmonosaccharides and disaccharides and amino acids, as well ascombinations thereof.
 28. The carrier system of claim 20, wherein therelease-controlling substance is selected from among polymers of theclass of the hydrogel-forming polymers, the polysaccharides, theproteins and peptides, the polyethers and polyesters, an electrolyte andmonosaccharides and disaccharides and amino acids, as well ascombinations thereof.
 29. The carrier system of claim 21, wherein therelease-controlling substance is selected from among polymers of theclass of the hydrogel-forming polymers, the polysaccharides, theproteins and peptides, the polyethers and polyesters, an electrolyte andmonosaccharides and disaccharides and amino acids, as well ascombinations thereof.
 30. The carrier system of claim 22, wherein therelease-controlling substance is selected from among polymers of theclass of the hydrogel-forming polymers, the polysaccharides, theproteins and peptides, the polyethers and polyesters, an electrolyte andmonosaccharides and disaccharides and amino acids, as well ascombinations thereof.
 31. The carrier system of claim 23, wherein therelease-controlling substance is selected from among polymers of theclass of the hydrogel-forming polymers, the polysaccharides, theproteins and peptides, the polyethers and polyesters, an electrolyte andmonosaccharides and disaccharides and amino acids, as well ascombinations thereof.
 32. The carrier system of claim 24, wherein therelease-controlling substance is selected from among polymers of theclass of the hydrogel-forming polymers, the polysaccharides, theproteins and peptides, the polyethers and polyesters, an electrolyte andmonosaccharides and disaccharides and amino acids, as well ascombinations thereof.
 33. The carrier system of claim 25, wherein the atleast one release-controlling substance is selected from the groupconsisting of polyethylene glycol and a hydrogel-forming polymer. 34.The carrier system of claim 26, wherein the at least onerelease-controlling substance is selected from the group consisting ofpolyethylene glycol and a hydrogel-forming polymer.
 35. The carriersystem of claim 27, wherein the at least one release-controllingsubstance is selected from the group consisting of polyethylene glycoland a hydrogel-forming polymer.
 36. The carrier system of claim 28,wherein the at least one release-controlling substance is selected fromthe group consisting of polyethylene glycol and a hydrogel-formingpolymer.
 37. The carrier system of claim 29, wherein the at least onerelease-controlling substance is selected from the group consisting ofpolyethylene glycol and a hydrogel-forming polymer.
 38. The carriersystem of claim 30, wherein the at least one release-controllingsubstance is selected from the group consisting of polyethylene glycoland a hydrogel-forming polymer.
 39. The carrier system of claim 31,wherein the at least one release-controlling substance is selected fromthe group consisting of polyethylene glycol and a hydrogel-formingpolymer.
 40. The carrier system of claim 32, wherein the at least onerelease-controlling substance is selected from the group consisting ofpolyethylene glycol and a hydrogel-forming polymer.
 41. The carriersystem of claim 1, wherein the at least one release-controllingsubstance is not of animal origin.
 42. The carrier system of claim 1,wherein the active substance is present in the carrier system in acontent of less than 10 wt. %.
 43. The carrier system of claim 1,further comprising at least one active substance.
 44. The carrier systemof claim 35, wherein the active substance is a problematic activesubstance.
 45. The carrier system of claim 1, wherein the weightincrease of the carrier system associated with swelling in water isbelow 20%.
 46. A pharmaceutical composition containing a carrier system,the carrier system comprising: at least one problematic activesubstance; at least one lipid matrix, the lipid matrix having asolubility in water of 1 part of lipid matrix in at least 30 parts ormore of water; and at least one release-controlling substance which isinsoluble in the lipid matrix.
 47. The pharmaceutical compositionaccording to claim 46, wherein the problematic active substance is amedicament based on proteins, peptides and antisense oligonucleotides.48. The pharmaceutical composition of claim 46, wherein the medicamentis selected from among a cytokine, growth factor, a cytostatic, insulin,hyaluronidase and erythropoietin.
 49. The pharmaceutical composition ofclaim 47, wherein the medicament is selected from among a cytokine,growth factor, a cytostatic, insulin, hyaluronidase and erythropoietin.50. The pharmaceutical composition of claim 46, wherein the activesubstance isD-arginyl-L-arginyl-L-prolylglycyl-3-(2-thienyl)-L-alanyl-L-seryl-(3R)-1,2,3-tetrahydro-3-isoquinolinocarbonyl-(2S,3aS,7aS)-octahydro-1H-indo-1-2-carbonyl-L-arginine.51. A method of using a carrier system to prepare a pharmaceuticalcomposition, comprising the steps of: preparing a carrier systemcomprising: at least one problematic active substance; at least onelipid matrix, the lipid matrix having a solubility in water of 1 part oflipid matrix in at least 30 parts or more of water; and at least onerelease-controlling substance which is insoluble in the lipid matrix;and using the carrier system to prepare the pharmaceutical composition.52. The method of claim 51, wherein the pharmaceutical composition isfor the parenteral administration of active substances.
 53. The methodof claim 51, wherein the pharmaceutical composition is for theadministration of an active substance by injection.
 54. The method ofclaim 51, wherein the pharmaceutical composition is for the in-vitro orin-vivo release of problematic active substances.
 55. The method ofusing a carrier system of claim 50, wherein the active substance is aproblematic active substance.
 56. The method of using a carrier systemof claim 51, wherein the active substance is a problematic activesubstance.
 57. The method of using a carrier system of claim 52, whereinthe active substance is a problematic active substance.
 58. The methodof using a carrier system of claim 53, wherein the active substance is aproblematic active substance.
 59. The method of using a carrier systemof claim 54, wherein the active substance is a problematic activesubstance.
 60. Use of lipids having a water solubility of 1 part oflipid to at least 30 parts or more of water for the stabilisation ofproblematic active substances.